This invention relates to gas turbines and specifically, to gas turbine shroud supports.
In a gas turbine engine, such as may be used for electrical power generation for example, in order to achieve enhanced engine efficiency it is desired that buckets rotate within a turbine case or “shroud” with reduced clearance to provide enhanced efficiency relative to an amount of energy available from an expanding working fluid. Typically, increased operation efficiencies can be achieved by maintaining a reduced threshold clearance between the shroud and tips of the buckets, which prevents unwanted “leakage” of hot gas over tips of the buckets. Increased clearances lead to leakage problems and cause reduction in overall efficiency of the turbine.
Ceramic matrix composites offer advantages as a material of choice for shrouds in a turbine for interfacing with the hot gas path. The ceramic matrix composites can withstand high operating temperatures and are suitable for use in the hot gas path of gas turbines. Recently, melt-infiltrated (MI) silicon-carbon/silicon-carbon (SiC/SiC) ceramic matrix composites (CMC) have been formed into high temperature, static components, such as gas turbine shrouds for example. Because of their heat capability, ceramic matrix composite turbine components, such as components made from MI-SiC/SiC components for example, generally allow for a reduction in cooling flow, as compared to metallic components.
It will be appreciated that the shrouds are subject to vibration due to pressure pulses of the hot gases as each bucket passes the shroud. Moreover, because of this proximity to high-speed rotating buckets, the vibration may be at or near resonant frequencies and thus require damping to enhance life expectancy during long-term commercial operation of the turbine. Ceramic composites require unique attachment and have multiple failure mechanisms such as wear, oxidation, stress concentration and damage to the ceramic composite when configuring the composite for attachment to the metallic components. Accordingly, there is a need for responding to dynamics-related issues relating to the attachment of ceramic composite shrouds to metallic components of the turbine to minimize adverse modal response.